1. Field of the Invention
The present invention relates to technologies for rotating, at an extremely low-speed of rotation, a motor that has a dead band.
2. Description of the Related Art
Conventionally a variety of motors, such as direct-current (DC) motors and alternating current (AC) motors have been used in computers and devices such as scanners and printers. Printers that use motors for feeding paper and for driving a carriage that carries a print head can be presented as an example. (See JP2001-219613A).
In the aforementioned devices, there is the need to rotate the motor at an extremely low speed. This is because in scanners, for example, rotating the motor for transporting the carriage at an extremely low-speed will increase the resolution with which an original is read while moving an image sensor, mounted on the carriage, at an extremely low speed.
Here the control of the speed of rotation of the motor is performed by adjusting the driving voltage that is applied to the motor. For example, for a DC motor, an extremely slow driving voltage would be applied to the motor in order to rotate the motor at an extremely low speed.
On the other hand, a motor often has a voltage range wherein the motor will not rotate (known as a “dead band”) because the torque produced in response to the driving voltage is less than the static frictional force. Consequently, if the motor is a DC motor and an extremely small driving voltage is applied to the DC motor in order to increase the scanning resolution, there is a possibility that the driving voltage will be in the range of the dead band, so that the DC motor will not turn.
This problem occurs not only when the motor for moving the carriage is a DC motor, but also in a variety of other motors, such as AC motors, that have dead bands. Moreover, this problem is not limited only to scanners, but also to motors that are used in other devices, where this problem may occur in any motor having a dead band if an attempt is made to rotate the motor at an extremely low-speed of rotation.